title: Kinetic characterization of an intestinal trefoil factor receptor.
abstract: OBJECTIVE
  To determine whether intestinal epithelial cells have a receptor for intestinal trefoil factor and characterize receptor-ligand binding kinetics.
  
  
  METHODS
  Radioligand binding assays were performed to characterize the binding kinetics between [(125)I]-labeled ITF and IEC-6, HT-29, Caco2 and HaCaT cells. The K d, Bmax and other kinetic variables describing the interaction between ITF and its potential receptors were determined.
  
  
  RESULTS
  Radioligand binding assays performed at 4 °C showed that the K d value for the association between [(125)I]-ITF and IEC-6, HT-29, and Caco2 cells were 1.99 ± 0.12 × 10(-9) M, 3.89 ± 0.42 × 10(-9) M, and 2.04 ± 0.17 × 10(-9) M, respectively. Bmax values were 1.17 ± 0.04 × 10(11), 3.97 ± 0.29 × 10(11), and 2.03 ± 0.08 × 10(11) sites/cell, respectively. The K i values for the interaction between IEC-6, HT-29, and Caco2 cells and non-labeled ITF were 20.98 ± 0.57 nM, 36.87 ± 3.35 nM, and 21.38 ± 0.93 nM, respectively, and the IC50 values were 25.21 ± 0.39 nM, 40.68 ± 0.27 nM, and 23.61 ± 0.25 nM, respectively. Radioligand binding kinetic results showed the association rate constants (k +1) for IEC-6, HT-29, and Caco2 cells were 0.22 ± 0.04 min(-1), 0.29 ± 0.04 min(-1), and 0.26 ± 0.05 min(-1), respectively, and the dissociation rate constants (k -1) were 0.06 ± 0.02 min(-1), 0.03 ± 0.01 min(-1), and 0.04 ± 0.01 min(-1), respectively. For the HaCaT cells, the K d was 4.86 ± 0.28 × 10(-8) M and B max was 5.81 ± 0.15 × 10(8) sites/cell, the very low specific binding between [(125)I]-ITF and these cells made it impossible to calculate binding kinetic parameters.
  
  
  CONCLUSIONS
  An ITF-specific receptor appears to be present on the three types of intestinal epithelial cells (IEC-6, HT-29, and Caco-2), and there may be no ITF receptor on epidermal cells.
authors.affiliation: State Key Laboratory of Trauma, Burns and Combined Injury, Institute of Burns of PLA, Southwest Hospital, Third Military Medical University, Chongqing, PR China.
authors.forename: Zhang
authors.initials: Z
authors.lastname: Yong
authors.forename: Wang
authors.initials: W
authors.lastname: Lin
authors.forename: Sun
authors.initials: S
authors.lastname: Yong
authors.forename: Liang
authors.initials: L
authors.lastname: Guang-Ping
authors.forename: Wu
authors.initials: W
authors.lastname: Dan
authors.forename: Lv
authors.initials: L
authors.lastname: Shang-Jun
authors.forename: Wu
authors.initials: W
authors.lastname: Wei
authors.forename: Peng
authors.initials: P
authors.lastname: Xi
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002460:Cell Line; D000078404:Epidermal Cells; D004847:Epithelial Cells / Q000378:metabolism; D006801:Humans; D020128:Inhibitory Concentration 50; D007413:Intestinal Mucosa / Q000378:metabolism*; D007700:Kinetics; D008024:Ligands; D011485:Protein Binding; D011869:Radioligand Assay; D051381:Rats; D018000:Receptors, Peptide / Q000378:metabolism*
chemical_list: D008024:Ligands; D018000:Receptors, Peptide; C108345:trefoil factor receptor